Method of producing a rotor

ABSTRACT

In rotors for electric motors, it is usual to fix the commutator on the rotor shaft by means of a press fit. In the present invention, the rotor shaft, with the rotor core fixed thereon, is electronically coated with an epoxy layer on opposite portions of the rotor shaft and in the winding slots, and is then heated on the plasticizing and curing temperature of the epoxy. After that, with the help of a sliding temperature, the commutator, whose inner bore has a clearance fit relative to the rotor shaft, is slipped onto the rotor shaft in a terminal position, in the process the still-viscous epoxy is pushed backward and is deposited radially on a connecting end face, forming a bead, and penetrates the annular gap between the inner bore and the rotor shaft. Once the epoxy layer has cooled, the commutator is fixed against rotation and displacement on the rotor shaft. The rotor is suitable for electric motors of various types.

This application is a division of application Ser. No. 09/171,534, filedOct. 21, 1998, now U.S. Pat. No. 6,249,957, which is a 371 ofapplication Ser. No. PCT/DE97/02839, filed Dec. 5, 1997.

PRIOR ART

The invention is based on a rotor and a method for producing a rotor. Arotor is already known (German Patent DE 37 28 000 C2), in which therotor core is covered by an end disk on each face end that, on its facetoward the rotor core and toward the rotor shaft has flow conduits, intowhich a winding impregnating agent can be introduced that after curinghas taken place serves as an additionally effective stabilizing agent.

ADVANTAGES OF THE INVENTION

The rotor according to the invention and the method according to theinvention for producing a rotor, respectively, has the advantage that afixation of the commutator is possible in a simple way by means of theinsulating agent (epoxy-based coating powder) applied to the rotor shaftand the rotor core. For that purpose, the inner bore of the commutatorcan be manufactured with a clearance fit or transition fit relative tothe rotor shaft, and as a result on assembly the commutator can beslipped, fitting smoothly onto the rotor shaft, and both damage to thesurface of the rotor shaft and internal stresses in the commutator areavoided, because the usual embodiment of the inner bore of thecommutator with a press fit relative to the rotor shaft in the prior arthas the danger of scratching the surface of the rotor shaft. Theinsulating layer applied moreover increases the axial retention forcesof the rotor core, as a rule built up from lamination sheets, on therotor shaft; that is, the rotor core is additionally mechanically heldby the insulating layer.

By means of the provisions recited herein, advantageous refinements ofand improvements to the rotor and the method disclosed are possible. Itis advantageous to embody the at least one recess of the commutator as aconical face that tapers from the connecting end face toward the innerbore, which makes easier penetration of the plasticized epoxy betweenthe inner bore of the commutator and the rotor shaft possible, whichleads to an improvement in the fixation of the commutator on the rotorshaft.

It is also advantageous to cover the rotor winding and the connectingwires, leading from the rotor winding to the commutator and joined tothe commutator, with a second sintered epoxy layer, which not onlyprotects against damage and aggressive media, but also effects anadditional fixation of the rotor winding, which in turn preventsvibration-caused breakage.

BRIEF DESCRIPTION OF THE DRAWING

One exemplary embodiment of the invention is shown in simplified form inthe drawing and described in further detail in the ensuing description.FIG. 1 shows a rotor with an epoxy layer; FIG. 2 shows a rotor with acommutator slipped onto the rotor shaft; FIG. 3 shows a commutator inlongitudinal section, taken along the line III—III in FIG. 4; FIG. 4shows a commutator of FIG. 3 in side view; and FIG. 5 shows a rotor witha second epoxy layer.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1 shows a rotor for an electric motor, having a longitudinal axis1, a rotor shaft 2 extending coaxially with it, and a rotor core 3slipped with a press fit coaxially onto the rotor shaft 2. The rotorcore 3 is a package of individual laminated sheets in a known manner,and has a plurality of winding slots 6, extending parallel to thelongitudinal axis 1, which as shown in FIG. 2 extend from a first endface 8, toward a commutator 7, to a second end face 9 of the rotor core3, remote from the commutator 7. The winding slots 6, the first end face8, and the second end face 9 of the rotor core 3, and a first portion 12of the rotor shaft 2 located between the rotor core 3 and the commutator7, as well as a second portion 13 of the rotor shaft 2, remote from thecommutator 7 and adjoining the rotor core 3, are covered with a centeredepoxy layer 14. For that purpose, the rotor, without the commutator, iscovered with masks in the regions of the rotor shaft 2 and rotor core 3that are not to be provided with an epoxy layer 14, and thethus-equipped rotor is introduced into coating system 17, indicated bydashed lines, in which electrostatically charged epoxy powder in afluidized powder bed is deposited on those regions of the rotor shaft 2and rotor core 3 that are not covered by masks, so that the portions 12and 13 of the rotor shaft 2, along with the first end face 8, the secondend face 9 and the winding slots 6 of the rotor core 3, are covered witha layer of epoxy powder. The outer jacket of the rotor core 3 is coveredas well. This powder layer on the outer jacket of the rotor core isremoved in an ensuing operation by means of blowing, suction orstripping, so that the outer jacket is powder-free. After that, thetemperature in the coating system 17 is increased until such time as theepoxy powder has heated up to its plasticizing and curing temperature,which is at approximately 240° C., and at which the epoxy powder becomesa viscous mass. In this state, the commutator 7 is slipped by means of asliding tool 19, represented by dot-dashed lines, onto the rotor shaft 2that rests near its second portion 13 on a retaining stop 18, in such away that the viscous epoxy layer 14 present on the first portion 12 ofthe rotor shaft 2 partly curves radially outward in the manner of a bead22 on a connecting end face 23 of the commutator 7 and penetrates anannular gap formed between the circumference of the rotor shaft 2 andthe wall of an inner bore 24 (see FIGS. 3 and 4). Once the epoxy hascured and the rotor has cooled down, the commutator 7 is fixed in theaxial direction and secured against rotation solely by the epoxy 14 onthe rotor shaft 2. As shown in FIGS. 3 and 4, the commutator 7 has acommutator core 27 made of a duroplastic, which us surrounded by a metalconductor sleeve 28, made particularly from copper. The inner bore 24,which has a clearance or transition fit relative to the circumference ofthe rotor shaft 2, extends in the commutator core 27.

Beginning at the connecting end face 23, the commutator 7 has a recess29, which extends toward the inner bore in the direction of thelongitudinal axis and which is shown in FIG. 3 as a conical face 29tapering toward the inner bore 24. However, the recess 29 may also beembodied as a longitudinal groove leading to the inner bore 24. Therecess, for instance in the form of the conical face 29 that taperstoward the inner bore 24, makes easy, uniform penetration of the viscousepoxy into the annular gap formed between the rotor shaft 2 and theinner bore 24 possible. For better fixation of the commutator 7 in thedirection of rotation, indentations 32 in the commutator core 27 areprovided on the connecting end face 23 of the commutator 7, which forinstance begin at the recess 29 and extend as far as the circumferenceof the commutator core 27. The cross section of the indentations 32 maybe rectangular, triangular, semicircular, or the like. The bead 22 ofepoxy 14 radially covers the indentations 32 and digs into them.Commutator slots 33 extending in the direction of the longitudinal axissever the conductor sleeve 28 to form individual segments 34,electrically insulated from one another, that each have a respectiveconnecting hook 35 toward the connecting end face 23. One connectingwire 37 of the rotor winding 38 shown in FIG. 5 is electricallyconnected to each connecting hook 35 by clamping. Once the rotor winding38 has been inserted into the winding slots 6 of the rotor core 3 andthe connecting wires 37 have been connecting to the connecting hooks 35of the commutator 7, the rotor is reintroduced into the coating system17 and recoated electrostatically with epoxy powder on the rotor winding38 and the connecting wires 37, and then heated to the plasticizing andcuring temperature, as a result of which a second epoxy layer 39 issintered on that covers the rotor winding 38 and the connecting wires 37and thus fixes them; this improves both the resistance to jarring andthe protection against aggressive media. Naturally, the second epoxylayer 39 in the process is also deposited on the first portion 12 of therotor shaft 2 and on both the connecting end face 23 and the connectinghooks 35 of the commutator 7.

The foregoing relates to a preferred exemplary embodiment of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A rotor for an electric motor, comprising a rotorshaft, a rotor core, and a commutator, which are disposed coaxially to alongitudinal axis, the rotor core has winding slots with at least onerotor winding disposed therein and a first end face oriented toward thecommutator and a second end face remote from the commutator, and therotor shaft has a first portion located between the rotor core and thecommutator and a second portion beginning at the second end face of therotor core and remote from the commutator, and the commutator has both aconnecting end face oriented toward the rotor core and an inner borecoaxial with the longitudinal axis, the winding slots (6), the first endface (8), and the second end face (9) of the rotor core (3), as well asthe first portion (12) and the second portion (13) of the rotor shaft(2), are covered with a first sintered epoxy layer (14), and thecommutator (7) has at least one indentation (32) on its connecting endface (23) and, beginning at the connecting end face (23), at least onerecess (29) extending toward the inner bore (24) in the direction of thelongitudinal axis (1), and the first sintered epoxy layer (14), forfixation of the commutator (7), engages the at least one indentation(32), and also engages and filled the space which is formed between theat least one recess (29) and the shaft.
 2. The rotor according to claim1, characterized in that the at least one recess of the commutator (7)is embodied as a conical face (29) that tapers from the connecting endface (23) toward the inner bore (24).
 3. The rotor according to claim 2,in which the rotor winding (38) and the connecting wires (37), leadingfrom the rotor winding (38) to the commutator (7) and joined to thecommutator, are covered with a second sintered epoxy layer (39).
 4. Therotor according to claim 1, in which the rotor winding (38) and theconnecting wires (37), leading from the rotor winding (38) to thecommutator (7) and joined to the commutator, are covered with a secondsintered epoxy layer (39).